1. Field of the Invention
The present invention relates to a dynamoelectric machine in which a contacted part such as a slip ring, a commutator, etc., and a brush slide in contact, and particularly relates to a dynamoelectric machine such as an automotive alternator, an automotive electric motor, an automotive generator-motor, etc., provided with a rotation detecting apparatus for detecting a rotational position of a rotor.
2. Description of the Related Art
A conventional automotive generator-motor 100, as shown in FIG. 17, is provided with: a housing 101 composed of a generally cup-shaped front bracket 102 and rear bracket 103; a shaft 104 rotatably supported in the housing 101 by means of front-end and rear-end bearings 105 and 106; a rotor 107 fixed to the shaft 104 and rotatably disposed inside the housing 101; a stator 108 held by an inner wall surface of the housing 101 so as to surround the rotor 107; a pair of slip rings 109 disposed on an outer circumference of an end portion of the shaft 104 projecting beyond the rear-end bearing 106; a brush apparatus 110 disposed on an outer circumference of the slip rings 109; a rotor position detecting apparatus 111 for detecting a relative position of the rotor 107 relative to the stator 108; a rear cover 112 securely fastened to the rear bracket 103 so as to cover the brush apparatus 110 and the rotor position detecting apparatus 111; and a pulley 113 fixed to a front-end end portion of the shaft 104.
The rotor 107 is provided with: Lundell-type pole cores 115 fixed to the shaft 104; and rotor coils 116 installed in the pole cores 115.
The stator 108 is provided with: a stator core 117 disposed so as to be held between the front bracket 102 and the rear bracket 103 and surround the rotor 107; and a three-phase stator coil 118 installed in the stator core 117.
The brush apparatus 110 is provided with: a pair of brushes 119 sliding in contact with outer circumferential surfaces of the pair of slip rings 109; and a brush holder 120 for housing the brushes 119.
The rotor position detecting apparatus 111, as shown in FIGS. 18A, 18B, and 19, is provided with a magnetic pole holding plate 121, magnetic sensor poles 122, and a position sensor 123. The magnetic pole holding plate 121 is prepared into a disk shape using a ferromagnetic material, is securely fastened to a rear-end end surface of the shaft 104, and rotates with the shaft 104. The magnetic sensor poles 122 are constituted by an annular permanent magnet, being magnetized with South-seeking (S) poles and North-seeking (N) poles alternately at a uniform pitch in a circumferential direction. The magnetic sensor poles 122 are fixed to the magnetic pole holding plate 121 by means of an adhesive, etc., being disposed so as to cover a rear-end end portion of the shaft 104 in an annular shape. The position sensor 123 is constituted by a generally fan-shaped printed circuit board 125, etc., on which an electronic circuit including three Hall elements 124 is formed. The position sensor 123 is securely fastened to an end surface of the rear bracket 103 such that the Hall elements 124 face the magnetic sensor poles 122 in close proximity thereto.
Operation of the automotive generator-motor 100 constructed in this manner when used as an electric motor will now be explained.
During starting of an engine, an alternating current is supplied sequentially to each phase of the three-phase stator coil 118 by a three-phase drive circuit (not shown), and a direct current is supplied to the rotor coil 116 by means of the brushes 119 and the slip rings 109. Thus, the stator coil 118 and the rotor coil 116 become electromagnets, and the rotor 107 rotates inside the stator 108 together with the shaft 104. Torque from the shaft 104 is transmitted to an output shaft of the engine by means of the pulley 113, starting the engine.
At this time, the magnetic sensor poles 122 rotate together with the rotation of the shaft 104. Changes in magnetic flux due to rotation of the magnetic sensor poles 122 are detected by the position sensor 123 and output to an external control apparatus (not shown) as rotor position signals. The control apparatus into which the rotor position signals are input controls the alternating current supplied sequentially to each of the phases of the three-phase stator coil 118 such that the direction of rotation of the rotor 107 is constant and a predetermined rotational frequency is achieved.
Next, operation of the automotive generator-motor 100 when used as a generator will be explained.
When an engine is started, torque from the engine is transmitted to the shaft 104 by means of the pulley 113, rotating the shaft 104. Thus, when a direct current is supplied to the rotor coil 116 by means of the brushes 119 and the slip rings 109, the rotor coil 116 is excited and becomes an electromagnet. By rotating the rotor 107 inside the stator 108 in this state, an alternating current is induced sequentially in the stator coil 118 installed in the stator core 117 and a generated voltage rises rapidly. This three-phase alternating current is input into a three-phase rectifying circuit (not shown) and is rectified into a direct current. The direct-current voltage rectified by the three-phase rectifying circuit charges a battery and is supplied to an electric load.
In a conventional automotive generator-motor, because the brush apparatus 110 and the rotor position detecting apparatus 111 are disposed adjacent to an end portion of the shaft 104 projecting beyond the rear-end bearing 106 as explained above, one problem has been that abraded brush dust arising due to the sliding of the brushes 119 on the slip rings 109 may penetrate the gaps between the Hall elements 124 and the magnetic sensor poles 122 which are disposed in close proximity, preventing the rotor position detecting apparatus 111 from stably detecting the changes in the magnetic flux.
The present invention aims to solve the above problems and an object of the present invention is to provide a dynamoelectric machine enabling an angular position of a rotor to be detected with high precision by disposing contacts and a rotation detecting apparatus with a bearing interposed to prevent abrasion dust arising due to sliding motion between a contact and a contacted part from penetrating into the rotation detecting apparatus.
With the object in view, the dynamoelectric machine of the present invention includes a housing, a first bearing disposed in a first axial end portion of the housing, a second bearing disposed in a second axial end portion of the housing and a shaft rotatably supported in the housing by means of the first and second bearings. Further, the dynamoelectric machine includes a rotor composed of a rotor core fixed to the shaft and rotatably disposed inside the housing and a rotor coil installed in the rotor core, a stator composed of a stator core supported in the housing so as to surround an outer circumference of the rotor and a stator coil installed in the stator core, a contacted part fixed to an outer circumference of the shaft axially inside the first bearing and electrically connected to the rotor coil, and a contact disposed so as to contact an outer circumferential surface of the contacted part. Still further, the dynamoelectric machine includes a rotation detecting apparatus composed of a sensor rotor fixed to an end portion of the shaft projecting axially outside the first bearing, a sensor unit disposed in close proximity to the sensor rotor, and a connector unit for delivering input and output signals to and from the sensor unit.
Therefore, abrasion dust arising due to sliding motion between the contact and the contacted part does not penetrate into the rotation detecting apparatus, thereby providing a dynamoelectric machine enabling an angular position of the rotor to be detected with high precision.